Ncert Exercises & Solutions

9.19 [Cr(NH₃)₆]³⁺ is paramagnetic while [Ni(CN)₄]^2– is diamagnetic. Explain why?

Step 1:

In [Cr(NH₃)₆]³⁺, Cr is in the +3 oxidation state i.e., 3 $d^{3}$ configuration. Also, $N H_{3}$ is a weak field ligand that does not cause the pairing of the electrons in the 3d orbital. $C r^{3 +}$

Therefore, it undergoes $d^{2} s p^{3}$ hybridization and the electrons in the 3d orbitals remain unpaired. Hence, it is paramagnetic in nature.

Step 2:

In [Ni(CN)₄]^2-, Ni oxidation is +2 and its electronic configuration is 3d⁸ configuration.

${Ni}^{2 + =}$

$C N^{-}$ is a strong field ligand. Hence, it paired the 3d electrons. Then, $N i^{2 +}$ undergoes $d s p^{2}$ hybridization.

As there are no unpaired electrons, it is diamagnetic in nature.

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